Photographic elements having improved sensitivity



Aug. 15, 1961 G. w. LUCKEY ETAL 2,996,382

PHOTOGRAPHIC ELEMENTS HAVING IMPROVED SENSITIVITY Filed Jan. 12, 1959 F EMULSION LAYER SUPPORT GEORGE W LUCK E Y JOHN C. HOPPE INVENTORS ATTORNEYS atent Patented Aug. 15, 1961 nice 2,996,382 PHOTOGRAPHIC ELEMENTS HAVENG IMPROVED SENSITIVITY George W. Luekey and John C. Hoppe, Rochester, N.Y.,

assignors to Eastman Kodak Company, Rochester,

N.Y., a corporation of New Jersey Filed Jan. 12, 1959, Ser. No. 786,225 8 Claims. (Cl. 96--68) This invention relates to photographic elements having improved sensitivity, and more particularly, to photographic layers comprising both a surface latent image emulsion and a fogged internal image emulsion.

It is known that silver halide crystals of the type employed in photographic emulsions have both surface and internal sensitivitiy to light, and that these types of sensitivity may vary considerably among different emulsions. Silver halide crystals having a high ratio of surface-tointernal sensitivity comprise the silver halide grains used in the majority of photographic emulsions.

Silver halide grains having a high ratio of internalto-surface sensitivity are also well known but are less generally employed in practice. Emulsions containing such grains are described, for example, in Mees, The Theory of the Photographic Process, page 2211 (Revised Edition), 1954; in Journal of the Optical Society of America, 31 (1941), page 385, and in Davey and Knott U.S. Patent 2,592,250, issued April 8, 1952.

We have found that the sensitivity and contrast characteristics of the combination of various surface latent image emulsions with various internally fogged internal latent image emulsions is greater than that obtainable from either type of emulsion used alone. The particular surface latent image emulsions used in our invention have a relatively high degree of surface sensitivity and relatively low internal sensitivity, while the internal image emulsions used in our invention have a high degree of internal sensitivity but relatively low surface sensitivity.

Accordingly, it is an object of our invention to provide photographic elements having improved sensitivity. Another object is to provide coatings of photographic layers containing both a surface latent image emulsion and a fogged internal latent image emulsion. Another object of our invention is to provide a means for increasing the contrast of surface latent image emulsions having relatively low contrast. Other objects will become apparent from a consideration of the following description and examples.

The photographic layers used in our invention can comprise blends or mixtures of surface latent image emulsions and fogged internal image emulsions, or these two types of emulsions can be coated in contiguous layers of the photographic element. In coating the two types of emulsions in separate layers, either emulsion can be coated on top, since the fogged internal latent image emulsions have suflicient transparency to enable the surface latent image emulsion to be placed closest to the support and still receive sufficient transmitted radiation through the fogged internal latent image emulsions for exposure. Exposure of the emulsion closest to the support can also be made through the support where this is transparent. Alternatively, the two types of emulsions can be mixd as a blend and coated over an emulsion layer comprising a fogged internal image emulsion, which may be identical to or different from the fogged internal image emulsion in the blend. As shown in the examples below, an increase in speed can be obtained by such arrangements.

The photographic elements useful in our invention can be depicted as shown in the accompanying drawings, which are merely illustrative. -In FIG. 1, the latent image emulsion is mixed with the fogged internal latent image emulsion, whereas in FIG. 2 these two emulsions are coated in separate layers.

It appears that the improvement obtained in our invention occurs, at least in part, because the products resulting from the development of the surface latent imagebearing emulsion grains migrate to some of the nearby internally prefogged internal latent image emulsion grains and there uncover the internal fog centers, thus permitting the development of these grains with a consequent increase in mass of silver produced, density and even photometric equivalence of the image. These effects have been found to be outstanding in silver iodohalide surface latent image emulsions, such as ordinary silver bromiodide emulsions. Such emulsions can contain varying amounts of iodide, although we have found that especially useful results can be obtained with such iodo-halide surface latent image emulsions containing from about 0.5 to 99 mole percent iodide. The important product produced by the development of such surface latent irnage-bearing emulsions appears to be the iodide ion.

The emulsion combinations'of our invention have been found to provide speed increases when processed in developers having moderately high silver halide solvent action, as well as in developers having little or no silver halide solvent activity. This is shown in the examples below. It is immediately apparent that the silver halide solvent action of the developer should not be too high, for the fogged internal image emulsion would then become spontaneously developable, resulting in overall fog. If an appropriate amount of silver halide solvent is used in the developer, the fogged internal image emulsion then develops only in the regions Where the exposed, but unfogged, surface image grains develop, resulting in the improvements illustrated in our invention.

The surface image emulsions useful in our invention comprise those which, when measured according to normal photographic testing techniques by coating a test portion of the emulsion on a transparent support, exposing the test portion to a light intensity scale for a fixed time between 0.01 and 1 second and development for 6 minutes at 68 F. in Developer A as hereinafter defined, have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of the same emulsion which has been exposed in the same way, bleached 5 minutes in aqueous 0.3 percent potassium ferricyanide solution at F., and developed for 5 minutes at 65 F. in Developer B as hereinafter defined. Developer A is the usual type of surface image developer and Developer B is an internal developer having high silver halide solvent activity. The degree of internal sensitivity of the surface image emulsions is not particularly critical. The surface image emulsion can have relatively little internal sensitivity or it may have a fair amount of internal sensitivity, but

preferably not greater than the surface activity. Suitable surface image silver iodo-halide, e.g., silver bromoiodide, emulsions can be prepared by the method described by Trivelli and Smith in The Photographic Journal, volume LXXX, July 1940 (pages 285-288).

The surface image emulsions useful in practicing our invention include the well-known class of silver bromiodide emulsions. Such emulsions can advantageously contain 0.5 mole percent or more iodide. Such bromiodide emulsions can contain some chloride. The bromiodide emulsions useful in our invention comprise many of the high-speed negative types of silver bromiodide emulsions. These emulsions can have high or low contrast, and useful effects have beenobt-ained with both types of emulsions. The surface image emulsions useful in our invention can also be characterized as having a D greater than about 0.50 when the emulsion is coated at a coverage of about 540 mg. of silver per square foot, exposed to a stepwedge and processed for 12 minutes in Developer G as hereinafter defined.

The internal image emulsion useful according to our invention is one which, when measured according to normal photographic techniques in its unfogged stage .by coating a test portion of the emulsion on a transparent support, exposing to a light intensity scale having a fixed time between 0.01 and 1 second, bleaching 5 minutes in a 0.3% potassium fern'cyanide solution at 65 F. and developing for about 5 minutes at 65 F. in Developer B, has a sensitivity, measured at a density of 0.1 above fog, appreciably greater (e.g., at least 1.4 log E greater) than the sensitivity of an identical test portion which has been exposed in the same way and developed for 6 minutes at 68 F. in Developer A. Several suitable emulsions of this type are described in Davey and Knott U.S. Patent 2,592,250, issued April 8, 1952, but it is to be understood that other emulsions, which need contain no silver iodide, can be used in our invention. Silver chlorobromide emulsions of the internal latent image types, as well as other varieties of internal latent image emulsions, can be used in our invention. Silver chlorobromide emulsions useful in our invention comprise those containing only chloride and bromide as the halides, or alternatively, other halides, such as iodide, can also be present.

Of course, the internal image emulsions usefiul in our invention must be fogged, partly-or completely, before use. The fogging should be suflicient to give. a density of at least 0.50 when one mole (AgX) of the fogged emulsion is co'ated in a blend with 3 moles of surface image emulsion at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in Developer B above. The surface D of the unfogged' internal image emulsions should be less than about 0.30 when the emulsions are exposed to D and processed for 8 minutes in Developer G, as identified below.

The fogging of the internal image emulsions useful in our inventioncan be effected by merely exposing the emulsions to light; or other methods, such as chemical fogging methods, can be used. The emulsions having high-internal fog but low surface sensitivity can be prepared by fogging an emulsion having both internal and surface sensitivity and then bleaching the surface image with av solution of potassium ferricyanide. Another means of obtaining our fo'gged internal image emulsions is by exposure of non-fogged internal image emulsions to high. energy radiation, such as X-rays.

The surface image emulsions used in our invention can be sensitized chemically by methods which have been previously described in the prior art, and these emulsions can be optically sensitized and can contain well-known antifoggans and development accelerators.

The ratio of the surface latent image emulsion to the fogged-internal image emulsion can be varied, depending uponflthe types of emulsions used, the contrast of the emulsions and other known variables. In general, quite useful results are obtained in those cases where the molar ratio of the surface image emulsion is at least equal to or greater than that of the fogged internal image emulsion. Useful results have been obtained even where the molar ratio, as explained above, was 42:1. Where the molar percent of the fogged internal image emulsion exceeds that of the surface image emulsion, such as a 1:3

ratio of surface to fogged internal image emulsion, there is some loss of speed although the contrast of the combination is considerably greater than that of the surface latent image emulsion. Accordingly, useful results have been obtained where the molar ratio of surface to fogged internal image emulsions varies from about 42:1 to 1:3.

These useful effects are illustrated in the examplm given below.

The following developing solutions are used in the method described in this application:

Grams A. N-methyl-p-aminophenol sulfate 0.31 Sodium sul-fite, desiccated 39.6 Hydroquinone 6 Sodium carbonate, desiccated 18.7 Potassium br mid 0.86 Citric acid 0.68 Potassium metabisulfite 1.5 Water to 1 liter.

B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated Hydroquinone 8.0

Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate 10 Water to 1 liter.

C. N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid l0 2-diethylaminoethanol 25 Potassium bromide 1 Sodium'carbonate, monohydrate 55.6 Water to 1 liter.

D. Same as C with addition of 15 grams of sodium sulfite per liter.

E. Same as C with addition of 30 grams of sodium sulfite per liter.

F. Same as B without the sodium thiosulfate.

G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite, desiccated 30 Hydroquinone 2.5

- Sodium metaborate 10 Potassium bromide 0.5 Water to 1 liter.

The improvements obtained by the addition of fogged internal image grains to the emulsions of the surface image type are illustrated by the following examples:

Example 1' A gelatino-silver-bromiodide emulsion (emulsion No. 1 below) having high surface sensitivity and low internal sensitivity was prepared according to the method described in Yutzy et a1. U.S. Patent 2,614,928, issued October 21, 1952 (see example 1), (or alternatively by Nietz et a1. U.S. Patent 2,222,264, issued November 19, 1940).

This bromiodide emulsion was mixed or blended with an emulsion (emulsion No. 2 below) having high internal sensitivity prepared by light fogging a gelatino-silverchlorobromiodide emulsion made essentially as described in Example 1 of Davey et al. U.S. Patent 2,592,250, issued April 8, 1952.

The surface and internal sensitivities of these emulsions were measured by the technique described above. The results are shown in the following table:

Internal Sensi- Surface Sensitivity-Bleach 1 tivity6 Dev. A Log E Emulsion No. +5 Dev. B F Log E at Surface- Log E at D=0.1 D=0.1 above Internal above Fog g 2 0.11 1. 40 l.28 (i.e.,

more negative).

l Bleach=bathed for at 65 F. in a 0.3% aqueous solution of potassium ferricyanide and then dried.

Coatings were made of the separate emulsions and also of the unfogged internal image emulsion and of various blends of the surface emulsion and fogged inter- The coated emulsions were exposed on an intensity scale sensitometer and processed at 68 F. with vigorous agitation of the solution, in the developers indicated below.

No image or fog was produced when exposed coating 2 (unfogged internal image emulsion) was developed for 5 minutes in Developer C, E or G. No image was produced when exposed coating 3 (fogged internal image emulsion) was developed in these same developers. The fog density was found to increase with increasing time of development when emulsion 3 was developed in these same developers.

When coating 1 (surface image emulsion) was exposed in the same way as emulsion 2 and was developed for 5 minutes in Developer G, it had a relative speed of 100 and fog density of .07. Under the same conditions coating 4 (3:1 blend of surface and fogged internal emulsion) had a relative speed of 130 and fog density of .11. The relative speed and fog for an emulsion blend similar to that used in coating 4 but in which the fogged internal image grains were replaced by unfogged internal image grains had a relative speed of only 89 and fog of .06. Thus, it is essential that the internal image emulsion be fogged in order to obtain the speed increase.

Substantial increases in gamma and density were obtained with these blended emulsions, and these increases became larger as the proportion of fogged internal image grains was increased and the silver halide solvent activity and antioxidant content of the developer were increased to optimum. Some of the these results are shown in the following table:

These results show that large increases in gamma and maximum density can be obtained without great increase in fog or much speed loss. Best results are obtained when the sodium sulfite concentration is not large enough to cause solution and development of the fogged internal image emulsion grains in unexposed areas of the fogged emulsion.

Example 2 A fogged internal image type emulsion prepared essentially as described in Example 1 of US. Patent 2,592,250 was mixed with a high-speed silver bromiodide emulsion which had been sulfur-and-gold sensitized and which had sun-face and some internal sensitivity. The log E difference between surface and internal sensitivity of this latter emulsion when determined by the method described in Example '1 above was 0.90 (A log E). The average grain size of the surface image emulsion was larger than that of the emulsion used in Example 1 above, and the emulsion contained 6 mole percent iodide. The emulsions were blended in a ratio of 3 parts of surface image grains to 1 part of fogged internal image grains, based on the equivalent of silver in the emulsions. This emulsion blend was coated on film base and designated coating No. 8. A similar coating was made of the surface emulsion alone and designated coating No. 7. This was coated with the same total silver coverage as in coating No. 8.

Both of these coatings were exposed for second on an Eastman Ib sensitometer and processed for 5 minutes at 20 C. in Developer G. The results were as follows:

Relative Coating Exposure Fog and Gamma Dmu S eed 0.2 Number Conditions Base bove Fog Example 3 In this example, high-speed coarse-grain latent image emulsions were prepared by running a silver nitrate solu tion into a gelatin solution containing potassium bromide and potassium iodide. The iodide level was varied to produce the mole percent iodide indicated in each case. The emulsions were washed and sulfur and gold sensitized, e.g., as described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, and Yutzy and Leermalcers US. Patent 2,597,915, issued May 27, 1952. Each latent image emulsion was coated alone and in a blend with a fogged internal latent image emulsion. The two emulsions were also coated as separate contiguous layers on the same support. The blends contained three parts of the latent image emulsion to one part of the fogged internal image emulsion, and the controls and the blends were coated at a total coverage of 200 sq. ft./mole of silver halide. In the two-layer coatings, the fogged internal image emulsion was coated at a coverage of 1200 sq. ft./mole of silver halide. Over this emulsion was coated the iatent image emulsion at a coverage of 200 sq. ftJmole of silver halide. In each case, the fogged internal image emulsion was a chlorobromiodide emulsion essentially of the type described in Davey et al. U.S. Patent 2,592,250, issued April 8, 1952. Several samples of each coating were exposed to a step wedge on an Eastman Ib sensitometer and developed at 68 F. for the indicated times in Developer G with the following results.

Approxi- 3' devel. 5 devel. 8' devel. 12 devel.

ma Mole Coating Percent Type of N 0. Iodide of Coating Rel. Rel. Rel. Rel.

. Latent Spd. 'y Fog Spd. 'y Fog Spd. 7 Fog Spd. 'y Fog Image Emulsion 0. 5 Check. 100 52 23 212 79 28 236 93 36 239 85 50 0. 5 Blend 67 48 10 173 77. 14 247 1. 01 .20 293 1. 24 34 0. 5 191 63 06 259 92 10 290 1. 05 17 282 1.07 33 1. 147 47 28 288 65 34 327 83 38 321 80 47 1.0 100 43 O9 212 63 12 290 .80 18 373 83 33 1. 0 233 55 .05 333 82 08 364 1.01 15 370 1.03 26 2. 167 53 12 288 69 13 333 84 .14 346 88 17 2. 5 103 41 05 282 69 07 403 1. 04 12 483 1. 22 28 2. 5 243 52 05 324 69 07 390 97 454 1. 36 3.0 173 37 11 240 69 12 309 88 14 324 92 16 3. 0 124 39 06 340 69 10 460 1. 06 22 521 1. 00 53 3. 0 233 51 06 309 65 08 421 93 10 515 1. 23 l5 5. 0 160 46 10 233 61 12 306 85 14 333 96 16 5. 0 103 89 07 343 63 13 480 99 533 1.02 70 5.0 191 49 06 297 61 08 403 92 11 503 1. 16 18 7. 0 121 l 43 08 250 59 10 321 89 .11 350 1. 09 13 7. 0 141 .37 10 340 54 .31 447 76 66 454 .82 1. 12 7. 0 163 44 08 300 56 11 418 84 20 471 1. 08 46 10. 0 73 37 10 218 54 13 321 76 14 358 92 16 10. 0 Blend 115 38 14 833 48 46 409 63 94 387 70 1. 33 10. 0 2-Layert 133 38 07 294 50 17 393 77 41 433 1. 06 73 Example 4 used. They were blended 1n the ratios indicated. The

In this example, a fogged chlorobromide internal image emulsion was used in the place of the fogged chlorobromiodide emulsion described in Example 3. The

fogged internal image chlorobromide emulsion contained 50 mole percent chloride, 50 mole percent bromide, and was prepared in the following manner:

An aqueous solution containing approximately 25 5 grams of a gelatin derivative of the type described in Yutzy and Frame US. Patent 2,614,928 was prepared. In this solution were dissolved slightly more than 1 mole of alkali halides consisting of potassium chloride and potassium bromide. The temperature of the solution was raised to approximately C. 'One mole of silver nitrate, dissolved in Water, was rapidly run into the alkali halide solution overa period of about 2 minutes with rapid stirring. The mixture was then held for about 8 minutes. At this point, the emulsion was coagulated and washed by the procedure described in US. Patent 2,614,- 928. The washed internal image emulsion was fogged by exposing the rapidly stirring liquid emulsion to a No. 2 Photoflood for 5 minutes. The light of the Photoflood was filtered through a No. 2-B filter, i.e., a filter transmitting only radiation beyond about 390 ru The 'fogged internal image emulsion was blended with a high- Coating No. Type of Relative 7 Fog Coating Speed (0) Check---" 100 0. 85 10 (b) B1end. 203 l. 55 25 Example. 5

This example shows how the ratio of the latent image emulsion to the tagged internal image emulsion can be varied and still obtain the desired improvement.

Part A.-The emulsions described in Example 4 were coatings were exposed on an Eastman Ib sensitometer and processed as described in Example 4 with the following results:

Ratio of Surface Image Coating N o. Emulsion to Relative 'y Fog Fogged In- Speed ternal Image Emulsion Part B.-The emulsions described in Example 3 were used, and they were blended in the ratios indicated. In all cases, the latent image emulsion was coated at a coverage of 180 sq. ft./mole of silver halide. The coatings were exposed on an Eastman Ib sensitometer and processed for 8 minutes in Developer G wtih the following results:

Ratio of Sur- 7 face Image Coating No. Emulsion to Relative 'y Fog V Fogged In- Speed ternal Image Emulsion It has been found that a useful speed increase can be obtained according to our invention by blending emulsions of the type described and processing them in a developer containing relatively small amounts of silver halide solvents. For example, the emulsions of Example 3 above were blended in a ratio of 3 parts of the latent image emulsion to 1 part of the fogged internal image emulsion. The emulsions were coated on a cellulose acetate support at a coverage of 1 mole of silver halide per 280 square feet. The coatings were exposed in an intensity scale sensitometer and processed for 12 minutes in the developer for Eastman Color Negative Film, Code 52 18 (Hanson and Kisner-Soc.. Mot. Pic. TV Eng.,. vol; 61, page 683, 1953), except that thedeveloper formula was adjusted to contain only 2 grams of sodium sulfite per liter and grams of ascorbic acid were added, and the pH was adjusted to 10.8. As compared with the sensitivity of the surface image emulsion, the emulsion blend had a senisitivity of 0.32 log E units greater than said surface image emulsion. Also, the emulsion blend had a gamma of 1.3 against .68' for the surface image emulsion, while the fog of the emulsion blend was .32 against a .21 for the surface image emulsion.

Example 6 This example shows that it is not necessary to fog the internal image emulsion to D in order to obtain an appreciable contrast or speed increase according to our invention. In this example, the internal image emulsion was fogged by exposing the liquid emulsion while stirring for the indicated times to a Photoflood filtered through a vN0. 2B filter. The surface image emulsion used in this example was a high-speed silver bromiodide emulsion which had be sulfur andgold sensitized as described in Example 3. The internal image emulsion was prepared by the procedure described in US Patent 2,592,250 except that the iodide was omitted. Three parts of the surface image emulsion was blended with one part of the fogged internal image emulsion. In each case, the emulsion was coated at a total coverage of 540 mg. of silver per square foot. A sample of each coating was exposed on an Eastman Ib sensitometer and processed as described below with the indicated results.

a-surface D up to the order of about 0.3. Two fogged internal'irn'age emulsions were preparedby the technique described in U.S. Patent 2,592;250, except that the iodide was omitted and the precipitation times and tempera- 5 tures were decreased in order to givea finer grain emulsion. The emulsion was fogged bythe procedure described above in Example 6.

Part A.A sample of the first fogged internal image emulsionwas coated on a cellulose acetate support at a coverage of 135 mg. of silver per square foot. A sample of this coating was processed 8 minutes. in Developer. G to give the surface D and a second. sample. was bleached 5 minutes in an aqueous 0.3% potassium ferricyanide solution at 65 F. andthen processed 5 minutes in Developer B to give the internal fog level with the following results:

Coating No. Internal FogLevel Surface max Developed 8 Minutes in D of Unex- Ratio of Surface Fog Time Developer G posed Film Coat Image Emulfor Internal Processed ing sion to Fogged Image 5 Minutes in No. Internal Image Emulsion Rela- Developer 13 Emulsion tive Gamma Fog Dm, (Internal Fog) Speed 3:1 2 seconds 229 1. 42 16 2. 85 3:1 8 seconds. 265 2. 39 18 3. 1 1.37 3:1 seconds--- 282 2. 94 20 3. 4 l. 67 1:0 check 100 1.23 .14 2.1 12

Example 7 posed on an Eastman Ib sensitometer and processed for This example shows that it is possible to use a surface image emulsion with a very low contrast and, by blending it With a fogged internal image emulsion, obtain a large increase in contrast as well as a speed increase. The surface image emulsion used in this case was a silver bromiodide emulsion containing 5 mole percent bromide andv95 mole percent iodide. The surface image emulsion was blended with a fogged internal image chlorobromide emulsion prepared by the'procedure used above in Example 6. The emulsions were coated on a cellulose acetate support at a total coverage of 540 mg. of silver per square foot. A sample of each coating was exposed on an Eastman Ib sensitometer and processed for 12 minutes in Developer G with the followingresults:

8 minutes in Developer G with the indicated results:

Ratio of Surface Image Coating N o. Emulsion to Relative Gamma Fog Fogged In- Speed ternal Image Emulsion Part B.-The second fogged internal image emulsion was coated on a cellulose acetate support at a coverage of 135 mg. of silver per square foot. The surface D and internal fog level were determined as described in gg g ggfge Relative Part A with the following results: Coating No. sion to Fogged Speed Gamma Fog D a Internal Image Emulsmn Coating No. Surface Internal Fog Level (11) 1:0 100 .32 .04 .80 (b) 3:1 871 2. 32 .12 2.80 (a) 28 1.50 Example 8 This example shows that it is possible to use for the fogged internal image emulsion an emulsion which has A sample of this fogged emulsion was blended with the surface image emulsion described in Part A, The

aeoassa o 12 Eastman Ib sensitometer and processed for minutes in Developer G with the following results:

Ratio of su r iiii riii i e coating N6. iig i g Relative Gamma Fog Coating No. Enulsign to Relative Gamma Fog Fogged In- Speed t i In Speed ternal Image ifi g fg Emulsion 1:0 97 1. 4s .07 53:33:::::::::::::::: is? 22 all Iii 3;} {g3 g3; j; 1:3 57 2.26 .16

Example 9 lfirlitelrflnsal Imtage This example further illustrates that it is possible to iog gii u use low-contrast surface image emulsions having a relatively low D and by means of our invention increase a1 82 1.24 .06 the D and contrast to a considerable extent. 1:1 65

A high-speed sulfurand gold-sensitized surface image emulsion was blended withda flogged internal ir1n-ag6e BIIVPIIII- E l 11 sion of the t e describe a ove in Exarnp e e emulsions weie coated on a cellulose acetate support at 2 example that lower total fog lellels and a total of 200 square feet per mole of silver halide. A L 9 contrast Y no loss speed can .sometmles be sample of each coating was exposed on an Eastman 1b 0 tained by coatmga surface 1mage-foggedmternal mage sensitometer and processed for 5 minutes in Developer 5 i blendpver a layer at fogged i l Image G with the following results: emulsion. high-speed sulfurand gold-sensitized silver bronuodlde emulsion was blended mm a fogged internal image emulsion of the type described above in Ratio of Sur- V Example 6. This blend was coated alone and also over a Coating i Relative Gamma Fog Dam layer of the fogged internal image emulsion. A sample Fogged In- Speed of each coating was exposed on an Eastman Ib sensi- Eliza? tometer and processed for 12 minutes in Developer G with the following results:

(a) 110 100 .24 1.84 (b) 311 214 50 Ratio of Surface Coating Image Emulsion Coverage (sq. Rela- No. to Fogged InftJmole of Silver tive Gamma Fog A coarse-grained, high-speed sulfurand gold-sensil m s al de) Speed tized emulsion having a very low contrast and D m sion was blended with a fogged internal image emulsion of 100 96 09 the type described above in Example 6. The emulsions 651 I were coated on a cellulose acetate support at a coverage 31 200 V of 200 square feet per mole of silver halide. A sample 'w Emul. Bottm Emu1 6 6 1.92 .25 of each coating was exposed on an Eastman lb sensitom- Si0110=1- sion 1,200-

Ratio of Surface Image Emulsion to Fogged Internal Image Emulsion Relative Speed Coating N0. Gamma Fog 1311153 Example 10 This example shows that it is possible to use blends containing more of the fogged internal image emulsion than the surface image. emulsion and still obtain a sub stantial contrast increase, although when the amount of the fogged emulsion exceeds the amount of the surface image emulsion some speed loss is usually encountered, probably because the fogged emulsion absorbs a considerable amount of incident light. This example also shows that when the internal image emulsion is unfogged, the increase in contrast and speed is not obtained.

A relatively high-speed silver bromiodide emulsion was blended with a fogged internal image emulsion and separately as well, with an unfogged internal image emulsion in the ratios indicated. The internal image emulsion was prepared bythe procedure described in U.S. Patent 2,592,250 and fogged as described above in Example 6. The emulsions were coated on a celluloseacetate support at a total coverage of 200 square feet per mole of silver halide. -A--sample of each coating was exposed on an The emulsion combinations useful in our invention and photographic elements containing them are illustrated in the accompanying drawings. FIG. 1 illustrates a pho tographic element comprising a support 10 and a photographic silver halide emulsion layer 11 comprising unfogged surface latent image grains 12 and fogged internal image grains 13.

In FIG. 2 there is illustrated a photographic element comprising a support 10, a layer 14 comprising fogged internal image grains 13 and a layer 15 comprising unfogged surface image grains 12.

Thesupports useful in our photographic elements comprise conventional supports, such as paper, cellulose ester film, polyvinyl resin film, polyester film, etc., as well as non-flexible supports, such as glass. 7 Thesilver halide emulsions can be suspended in conventional emulsion vehicles, such as gelatin, hydrolyzed polyvinyl esters, hydrolyzed cellulose esters, gelatin derivatives of the type shown in U.S. Patent 2,614,928, and the like.

Our invention can be used to produce high-speed X- ray and negative materials, high contrast materials used in graphic arts work and color emulsions and positive emulsions with improved speed and contrast. X-ray emulsions require high-speed, reasonably high contrast, and high maximum silver density. In the past; these requirements were fulfilled by the use of large emulsion grains. The present invention can be used to obtain these characteristics by combinations made from fast negative "surface image emulsions and fogged internal image emulsions.

In color photography, it is known that improved definition can be obtained by coating the blue-sensitive layer nearest the support. In this case, the blue-sensitive emulsion has higher blue light speed than the red-sensitive and green-sensitive emulsions so that during exposure only the blue-sensitive emulsion is exposed by the blue light incident on the film. By using the present technique, a higher speed blue-sensitive emulsion can be made and better color separation thus obtained.

The unique effects illustrated in the above examples of our invention can sometimes be increased by variations in the developing compositions, as has been shown. For instance, use of a silver halide solvent in the developer for the emulsion combinations of our invention causes a marked increase in speed, particularly in those cases where the silver iodide content of the surface image emulsion is low. Silver halide solvents which can be used in the developers comprise not only the illustrated thiosulfate and sodium sulfite, but also water-soluble thiocyanates and water-soluble quaternary ammonium compounds, such as those illustrated in Welliver et a1. U.S. Patent 2,648,604, issued August 11, 1953. It has also been found that the addition of iodide ion to the developers can reduce the amount of iodide required in the surface image emulsions to produce the unique effects of our invention. For example, potassium iodide can be added to developers of the type described above to enhance their efiects, particularly in processing surface image emulsions having a low iodide content.

The ratios used in the above examples are all molar ratios, based on the quantity of silver halide in the respective emulsions.

The emulsion blends or coatings described above can be used for recording and measuring very small amounts or doses of gamma rays, such as might be encountered in dealing with the development of synthetic radio-isotopes. It is a matter of common knowledge that it is important to keep a close watch on the radiation to which the personnel working in such areas may be exposed. However, the dental X-ray films usually employed, for this purpose give very inexact measurements. The novel photographic elements and emulsions of our invention are particularly useful in measuring the amounts of gamma rays to which such technical personnel have been exposed. The exposed elements can be developed in a conventional developer, such as Developer G above and the density of the exposed film measured. It has been found that the novel elements of our invention are much more sensitive to changes in density than conventional dental X-ray films. For such purposes, it is convenient to use, as the surface image emulsion, one which has a rather high iodide content in order to obtain high contrast.

The surface image emulsions of our invention can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, and Sheppard et a1. U.S. Patent 1,623,- 499, issued April 5, 1927, and Sheppard and Brigham U.S. Patent 2,410,689, issued November 5, 1946.

The surface image emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948, and as antifoggants in higher amounts, as described in Trivelli and Smith U.S. Patents 2,566,245, issued August 28, 1951, and 2,566,263, issued August 28, 19,51.

The surface image emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,083, issued April 23, 1946, or stabilized with gold salts as described in Damschroder U.S. Patent 14 2,597,856, issued May 27, 1952, and Yutzy and Leermakers U.S. Patent 2,597,915, issued. May 27, 1952. Suitable compounds are potassium chloroaurite, aurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The surface image emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued. November 15, 1949), polyamines, such as diethylene triamine (Lowe and Jones U.S. Patent 2,518,698, issued August 15, 19 50), polyamines, such as spermine (Lowe and Allen. U.S. Patent 2,521,925, issued September. 12, 1950), or bis([3- aminoethyl)sulfide and its water-soluble salts (Lowe and Jones U.S. Patent 2,521,926, issued September 12, 19 50).

The surface image emulsions can also be optically sensitized with cyanine and merocyanine dyes-as indicated above, such as those described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854, issued January 9, 1934; White U.S. Patent 1,990,507, issued February. 12, 1935; Brooker and 'White U.S. Patents 2,112,140, issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,- 747, issued January 10, 1950; and 2,739,964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950 and 2,519,001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; Heseltine U.S. Patent.2,734,900, issued February 14, 1956; Van Lare U.S. Patent 2,739,- 149, issued March 20, 1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.

The emulsion blends can also be stabilized with the mercury compounds of Allen, Byers, and Murray U.S. Patent 2,728,663, issued December 27, 1955; Carroll and Murray U.S. Patent 2,728,664, issued December 27, 1955'; and Leubner and Murray U.S. Patent 2,728,665, issued December 27, 1955 the triazoles of Heimbach and Kelly U.S. Patent 2,444,608, issued July 6, 1948; the azaindenes of Heimbach and Kelly U.S. Patents 2,444,605 and 2,444,- 606, issued July 6, 1948; Heimbach U.S. Patents 2,444,- 607, issued July 6, 1948and 2,450,397, issued September 28, 1948; Heimbach and Clark U.S. Patent 2,444,- 609, issued July 6, 1948; Allen and Reynolds U.S. Patents 2,713,541, issued July 19, 1955, and 2,743,181, issued April 24, 1956; Carroll and Beach U.S. Patent 2,716,062, issued August 23, 1955; Allen and Beilfuss U.S. Patent2,735,769, issued February 21, 1956; Reynolds and Sagal U.S. Patent 2,756,147, issued July 24, 1956; Allen and Sagura U.S. Patent 2,772,164,. issued November 27, 1956, and those disclosed by Birr in Z. wiss. Phot., vol. 47, 1952, pages 2-28; the quaternary benzothiazoliumcompounds of Brooker and Stand U.S. Patent 2,131,038, issued September 27, 1938; the disulfides of Kodak Belgian Patent 569,317, granted July 31, 1958; and the zinc and cadmium salts of Jones U.S. patent application Serial No. 493,047, filed March 8, 1955.

The surface image emulsions may also contain speedincreasing compounds of the quaternary ammonium type of Carroll U. S. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; and the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955.

The emulsion blends may contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alkane such as 1,5-pentane diol as described in Milton and Murray U.S. application Serial No. 588,951, filed June 4, 1956; an ester of an ethylene bis-glycolic acid such as ethylene bis(methyl glycolate) as described in Milton U.S. application Serial No. 662,564, filed May 31, 1957; his- (ethoxy diethylene glycol) succinate as described in, Gray U.S. application Serial No. 604,333, filed August 16, 1956, or a polymeric hydrosol as results from the.

r a 15 emulsion polymerization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrene-type compound as described in Tong U.S. patent application Serial No. 311,319, filed September 24, 1952. The plasticizer may be added to the emulsion before or after the addition of a sensitizing dye, if used.

The emulsion blends may be hardened with any suitable hardener for gelatin such as formaldehyde; a halo gen-substituted aliphatic acid such as mucobromic acid as described in White US. Patent 2,080,019, issued May 11, 1937; a compound having a plurality of acid anhydride groups such as 7,8-diphenylbicyclo-(2,2,2)-7-octene- 2,3,5,6-tetracarboxylic dianhydride, or a dicarboxylic or a disulfonic acid chloride such as terephthaloyl chloride or naphthalene-1,5-disulfonyl chloride as described in Allen and Carroll U.S. Patents 2,725,294 and 2,725,295, both issued November 29, 1955; a cyclic 1,2-diketone such as cyclopentane-l,2-dione as described in Allen and Byers U.S. Patent 2,725,305, issued November 29, .1955; a bisester of methane-sulfonic acid such as 1,2-di-(methanesulfonoxy)-ethane as described in Allen and Laakso U.S. Patent 2,726,162, issued December 6, 1955; 1,3-dihydroxymethylbenzimidazol-2-one as described in July, Knott and Pollak U.S. Patent 2,732,316, issued January 24, 1956; a dialdehyde or a sodium bisu-lfide derivative thereof, the aldehyde groups of which are separated by 2-3 carbon atoms, such as {E-methyl glutaraldehyde bissodiurn bisulfite as described in Allen and Burness U.S. patent application Serial No. 566,031, filed December 29, 1955; a bis-aziridine carboxamide such as trimethylene bis(l-aziridine carboxamide) as described in Allen and Webster U.S. patent application Serial No. 599,891, filed July 25, 1956; or 2,3-dihydroxy dioxane as described in Jeiireys U.S. patent application Serial No. 624,968, filed November 29, 1956. i

The internal or surface image emulsions may contain a coating aid such as saponin; a lauryl or oleoyl monoether of polyethylene glycol as described in Knoxand Davis U.S. Patent 2,831,766, issued April 22, 1958; a salt of a sulfated and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent No. 2,719,- 087, issued September 27, 1955; an acylated alkyl taurine such as the sodium salt of N-oleoyl-N-methyl taurine as described in Knox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a dianhydride of tetracarboxybutane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tctracarboxybutane' as described in Knox, Stenberg and Wilson U.S. patent application Serial No. 485,812, filed February2, 1955; a Water-soluble maleopimarate or a mixture of a watersoluble maleopimarate and a substituted glutamate salt as described in Knox and Fowler U.S. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodium N-(carbo-p-tert. octylphenoxypentaethoxy)glutamate as described in Knox and Wilson U.S. patent application Serial No. 600,679, filed July 30, 1956; or a sulfosuccinamate such as tetrasodium N-(1,2-dicarboxyethyl)-N-octadecyl sulfosuccinamate or N-lauryl disodium sulfosuccinamate as described in Knox and Stenberg U.S. patent application Serial No. 691,125, filed October 21, 1957.

As mentioned above, in the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide. in its preparation, gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe U.S. Patent 2,286,215, issued June 16, .1942; a far .hydrolyzedcellulose ester such as cellulose acetate hydrolyzedto an acetylcontent of 1926% as described in U.S. Patent 2,327,808

16, of Lowe and Clark, issued August 24, 1943; a watersoluble ethanolamine cellulose acetate as described in Yutzy,U.S. Patent 2,322,085, issued June 15, 1943; a polyacrylamidehaving a combined acrylamide content ofv 30-60% and a specific viscosity of 0.25-1.5 on an imidizedpolyacrylamide of like acrylamide content and viscosity as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474,, issued February 13, 1951; zein as described in Lowe U.S. Patent 2,563,791, issued August 7,1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith U.S. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest U.S. Patent 2,808,331, issued October 1,1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in U.S. application Serial No. 527,872 of Illingsworth, Dann and Gates, filed August 11, 1954.

If desired, compatible mixtures of two or more of these colloids may be employed .for dispersing the silver halide in its preparation. Combinations of these antifoggants, sensitizers, hardeners, etc., may be used.

The photographic elements or emulsion blends described above may be used in diflusion transfer processes ,Which utilize the undeveloped silver halide in the noniinage areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a receiving layer in close proximity to the silver halide emulsion layer. Such processes are described in Rott-U.S. Patent 2,352,014, issued June 20,1944, and Land U.S. Patents 2,584,029, issued January 29, 1952; 2,698,236, issued December 28, 1954, and 2,543,- 181, issued February 27, 1951; and Yackel et a1. U.S. patent application Serial No. 586,705, filed May 23, 1956. hey may also be used in color transfer processes which utilize the difi usion transfer of an image-wise distribution of developer, coupler or dye, from a light-sensitiverlayer to a second layer, while the two layers are in closeproximity to one another. Color processes of this type are described in Land U.S. Patents 2,559,643, issued July 10, 1951, and 2,698,798 issued January 4,-

1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; International Polaroid Belgian Patents 554,212, granted July 16, 1957, and 554; 935, granted August 12, 1957; Yutzy US. Patent 2,756,- 142, issued July 24, 1956, and Whitmore and Mader U.S. patent application Serial No. 734,141, filed May 9, 1958.

The addenda described above for use in conjunction withfour emulsions can beemployed in emulsions designed for X-ray photography, or in non-optically sensitized emulsions, or ortho-chromatic-, panchromaticor infra-rcd sensitized emulsions. They can be added before or aftersensitizingdyes are, added. These addenda can also be used in emulsions designed for color photography, for example, emulsions containing color-forming compoundsor couplers, .or emulsions to be developed in solutions containing such couplers, or emulsions of the mixed-packet type, such as described in Godowsky U.S. Patent 2,698,794, issued January 4, 1955, etc.

As indicated above, the emulsions having a high degree of internal sensitivity can be prefogged by means of light. It has. been foundin certain instances that a mottle-like effect is produced, due to a variation in the graininess pattern over an area of larger scale than the normal graininess pattern. The extent of the irregular mottle pattern of the imagecan be limited by superimposing a regular screen pattern, such as. a gravure tint or a, half-tone contact screen of the type used in the graphic arts industry, on the internally sensitive emulsion layer during the fogging operation with light. The surface sensitive emulsion can then be coated over the fogged internllly sensitive emulsion.

arise-see It has been found that the screen pattern can be made time enough (e.g., 150 lines per inch) so that the pattern 18 barely noticeable and the overall visual impression of the image is not adversely afiected. Some loss in speed and contrast may sometimes result from such a procedure, although the improvement in image quality more than offsets this insignificant loss of speed andcontrast.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A photographic element comprising a support and at least one lightssensitive photographic silver halide emulsion layer, said photographic element comprising unfog'ged surface image silver halide grains containing iodide (I) adjacent to fogged internal image silver halide grains (II), said unfogged surface image silver halide grains (1) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Water to 1 liter.

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test por tion of said emulsion containing unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

. Gr B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate -1 10 Water to 1 liter.

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated as a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium fenricyanide at 65 F. and developed for 5 minutes at 65 F. in developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of said emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in developer (A), said fogged internal latent image silver halide grains (11) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of unfogged surface latent image silver halide grains (I) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in developer (B).

2. A photographic silver halide emulsion blend having increased speed and producing images of increased contrast and density upon exposure to light :and development ina silver halide developer, comprising a mixture of an unfogged surface image silver halide emulsion con.- taining iodide (I), the silver halide grains of which are such as to cause a test portion of said unfogged surface image silver halide emulsion (I), when coated on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

to have a sensitivity, measured at a density of 0.1 above fog, at least 1.25 log E greater than the sensitivity of an identical test portion of said emulsion (I) which has been exposed in the same Way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 9 F. the following developer (B):

B. N-methyl-paminophenol sulfate 2.0 Sodium sulfite, desiccated Hydroquinone p 8.0 Sodium carbonate, monohydrate 52.-;5 Potassium bromide 5 Sodium thiosulfate 10 Water to 1 liter.

and a fogged internal image silver halide emulsion (-II), the silver halide grains of which in their unfogged cohdition, when coated as a photographic emulsion on a transparent support, exposed to a light-intensity scale for a fixed time between v.01 and l-second, bleached for 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in developer (B) has a sensitivity measured at a density of 0.1 above fog, at least 1.4 log E greater than the sensitivity of an identical test portionof said emulsion containing unfogged internal image silver halide grains which have been exposed in the same way and developed for 6 minutes at 68 F. in developer (A), said fogged internal image silver halide grains (II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of unfogged surface image silver halide grains (1) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in developer (B).

3. A photographic element comprising a support and a first discrete layer containing unfogged surface image silver halide grains containing iodide (I) and contiguous thereto a second discrete layer containing fogged internal image silver halide grains (II), said unfogged surface image silver halide grains (1) being such as to causes.

test portion thereof, when coated as a photographic silver halide emulsion on atransparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at I 1.5 'Water to l'liter.

a i t n t. squa e o t. and, proeessed 19 to.have a sensitivity, measured at a'density of 0.1' above .fog, greater than'the sensitivity of an identical test porztion 'of said'emulsion containing unfogged surface image silver halide grains (I) which has been exposed, in the same way, bleached minutes in aqueous 0.3% potassium 'ierricyanide solution at 65 F. and developed for 5 lites at 65 F. in the following developer (B):

fi m B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 i Hydroquinone 8.0 J; sodium'carbonate, monohydrate s 52.5 "Potassium 'bromide 5 g ,Sodium thiosulfaten- Water to'l'liter."

fogged internal image silver halide grains (11) being such-that-a test portion thereof, when coated as a silver halide emulsion in its unfogged condition'on a transparent support and exposed to a light-intensity scale for -'-a fixed time between .01 and 1 second, bleached 5 mini ites in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 in developer (B) has a sensitivity measured at a density of 0.1 above 'fog, greater the sensitivity of an identical test portion-of said emulsion containing unfogged internal image silver halide grains which'has been exposedin the same ay-and developed for 6 minutes at 68 F. in developer A), said foggedinternal latent image silver halide grains (11) having a density of at least 0.50 when one mole therepfis coated a blend with a photographic emulsion contan'ning 3 n1oles of unfogged surface latent image silver .halide grains (1) at ajtotalcoverage of about 540 mg. of for 5 minutes in developer (B). a

4. A photographic element comprising a support and at least one light-sensitive photographic silver halide -emulsion layer, said photographic element comprising un- -,fogged surface image silver halide grains containing from ';0.5 to.99 mole percent of iodide (I) adjacent to fogged internal image silver halide grains (II), said unfogged surface image silver halide grains (I) being such as to .cause a test portion thereof when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time be- .tween .01 and 1 second and development for 5 minutes at 68 F. in the following developer (A) Grams 'A. N-methyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone -e 6 Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to 1 liter.

' Grams *B. iN-methyl-p-aminophenol sulfate 2.0 V. Sodiumsulfite, desiccated .Q 90 Hydroquinone 8.0

, Sodiumcarbonate, monohydrate 52.5 Potassium .bromide -Q. 5

' Sodium thiosulfate 1o Waterto 1 liter.

said f ogged silver halide grains (11) being such, that attest portion thereof, when coated as'a silver halide emulsion in its unfogged condition on a transparent support and exposed to a' light-intensity scale for a fixed time'between ;01 and 1 second, bleached 5 utes in a 0.3% solution of potassium ferricyanideat F; and developed for- 5 minutes at 65 'F. in developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test "portion of said emulsion containing unfogged internal image silver halideg'rains which has been exposed in the same way and developed for 6 minutes at 68 F. in developer .(A), said fogged internal latent image silver halide grains (11) having a density of at least 0.50when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of unfogged surface latent image silver halide grains (I) at a total coverage of about 540mg. of silver per square foot andprocessed for ,5 minutes in developer (B). t,

5. A photographic element as defined in claim 4, said unfogged surface image silver halide grains (I), being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support at a total silver coverage of about 540 mg. per square foot, exposed to a step wedge and processed for 12 minutes in the following developer (G):

\ Grams G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite, desiccated 30 Hydroquinone 2.5 Sodium metabor 10 Potassium brnmide 0.5

Water to 1 liter. 7

has a-D greaterthan about 0.50.

I 6. .Aphotographicelementas defined in claim 4, said fogged internal image silver halide grains (II) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion in its unfogged condition on a transparent support, exposed to a step wedge and processed for 8 minutes in the following developer (G):

Grams G. N-methyl-p-aminophenol sulfate 2.5 Sodium sulfite, desiccated 30 Hydroquinone 2.5 Sodiuni metabor 10 Potassium bromide 0.5

Water to 1 liter.

has a D less than about 0.30.

7. -A photographic silver halide emulsion blend having increased speed and producing images of increased contrast and density upon exposure to light and development in a silver halide developer, comprising a mixture of an 'unfogged surface image silver bromiodide emulsion, the

silver bromiodide grains of which are such as to cause a test portion of said unfogged surface silver bromiodide emulsion, when coated on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 1.5 Water to 1 liter. l

to have a sensitivity, measured at a density of 0.1 above fog, at least 1.25 log E greater than the sensitivity of an identical test portion offsaid unfogged surface imageSiL verbromiodide emulsion which has beenexposed iuthe 21 same way, bleached minutes in an aqueous 0.3% potassium ferricyanide solution at 65 F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfate Water to 1 liter.

and a fogged internal image silver chlorobromide emulsion, the silver chlorobromide grains of which in their unfogged condition, when coated as a photographic silver halide emulsion on a transparent support, exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached for 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in developer (B), has a sensitivity measured at a density of 0.1 above fog, at least 1.4 log E greater than the sensitivity of an identical test portion of said emulsion containing unfogged internal image silver chlorobromide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in developer (A), said fogged internal image silver chlorobromide grains having a density of at least 0.50 when one mole thereof is coated in a. blend with a photographic emulsion containing 3 moles of unfogged surface image silver bromiodide grains at a total coverage of about 540' mg. of silver per square foot and processed for 5 minutes in developer (B).

8. A photographic element comprising a support and at least one light-sensitive photographic silver halide emulsion layer, said photographic element comprising unfogged surface image silver halide grains containing iodide (I) adjacent to fogged internal image silver halide grains (II), said unfogged surface image silver halide grains (1) being such as to cause a test portion thereof, when coated as a photographic silver halide emulsion on a transparent support and upon exposure to a light-intensity scale for a fixed time between .01 and 1 second and development for 6 minutes at 68 F. in the following developer (A):

Grams A. N-methyl-p-aminophenol sulfate 0.31 Sodium sulfite, desiccated 39.6 Hydroquinone 6 Grams Sodium carbonate, desiccated 18.7 Potassium bromide 0.86 Citric acid 0.68 Potassium metabisulfite 1.5

Water to 1 liter.

to have a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of said emulsion containing unfogged surface image silver halide grains (I) which has been exposed in the same way, bleached 5 minutes in aqueous 0.3% potassium ferricyanide solution at F. and developed for 5 minutes at 65 F. in the following developer (B):

Grams B. N-rnethyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5 Sodium thiosulfite 10 Water to 1 liter.

said fogged internal image silver halide grains (II) being such that a test portion thereof, when coated on a silver halide emulsion in its unfogged condition on a transparent support and exposed to a light-intensity scale for a fixed time between .01 and 1 second, bleached 5 minutes in a 0.3% solution of potassium ferricyanide at 65 F. and developed for 5 minutes at 65 F. in developer (B) has a sensitivity, measured at a density of 0.1 above fog, greater than the sensitivity of an identical test portion of said emulsion containing unfogged internal image silver halide grains which has been exposed in the same way and developed for 6 minutes at 68 F. in developer (A), said fogged internal latent image silver halide grains ('II) having a density of at least 0.50 when one mole thereof is coated in a blend with a photographic emulsion containing 3 moles of unfogged surface latent image silver halide grains (1) at a total coverage of about 540 mg. of silver per square foot and processed for 5 minutes in developer (B), the molar ratio of unfogged surface image silver halide grains to fogged internal image silver halide grains being from about 42:1 to 1:3.

References Cited in the file of this patent UNITED STATES PATENTS 2,456,955 Knott et a1. Dec. 21, 1948 

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND AT LEAST ONE LIGHT-SENSITIVE PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER, SAID PHOTOGRAPHIC ELEMENT COMPRISING UNFOGGED SURFACE IMAGE SILVER HALIDE GRAINS CONTAINING IODIDE (I) ADJACENT TO FOGGED INTERNAL IMAGE SILVER HALIDE GRAINS (II), SAID UNFOGGED SURFACE IMAGE SILVER HALIDE GRAINS (I) BEING SUCH AS TO CAUSE A TEST PORTION THEREOF, WHEN COATED AS A PHOTOGRAPHIC SILVER HALIDE EMULSION ON A TRANSPARENT SUPPORT AND UPON EXPOSURE TO A LIGHT-INTENSITY SCALE FOR A FIXED TIME BETWEEN .01 AND 1 SECOND AND DEVELOPMENT FOR 6 MINUTES AT 68*F. IN THE FOLLOWING DEVELOPER (A): 